1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to an image forming apparatus for printing a color image by sequentially operating a plurality of developers.
2. Description of the Related Art
Generally, an electrophotographic color image forming apparatus forms a color image by forming an electrostatic latent image on a photosensitive medium charged with a uniform electric potential by emitting a beam onto the photosensitive medium. The electrostatic image is developed with a toner of a predetermined color. The developed image is transferred and fixed onto print paper. Toner colors used in the color image forming apparatus are usually yellow (Y), magenta (M), cyan (C), and black (K). Therefore, four developing units are required to adhere the toners with the four colors on the electrostatic latent image.
Methods of forming a color image include a single path method in which four exposure units and four photosensitive media are used, and a multi-pass method in which a single exposure unit and a single photosensitive medium are used. A color image forming apparatus adopting the single pass method takes the same time for color printing and black and white printing, and thus, is usually used in a high-speed image forming apparatus. However, because it has four exposure units and four photosensitive media, the price of a color image forming apparatus adopting the single pass method is high. However, a color image forming apparatus operates at a relatively low speed and has a single photosensitive medium and a single exposure unit and adopts the multi-pass method in which exposing, developing, and transferring images are repeatedly performed for each of the colors to form a color image on an intermediary medium and then transferring the color image onto print paper.
In an image forming apparatus using the multi-pass method, the four developing units operate sequentially. Thus, a device for sequentially transmitting the rotational force of a driving motor to the four developing units is required. A conventional image forming apparatus includes four electronic clutches. The electronic clutches are expensive and result in an increased size of the image forming apparatus. Additionally, slipping occurs during a clutching operation, and thus, power is not timely transmitted.
Accordingly, a need exists for an improved image forming apparatus using a multi-pass method in which the plurality of developing units are selectively operated.